1. Field of the Invention:
The present invention relates to a process for the surface treatment of moldings based on polyamides by treatment with aqueous acids.
The present invention furthermore relates to moldings obtainable by this process and their use for metallization, ie. for coating with metals.
2. Description of the Background
Polyamides belong to the class consisting of the engineering plastics and are widely used in many areas.
In one interesting application, the area of metallized materials, polyamides have however largely not been used to date. This is due mainly to the inadequate adhesion of the metal layer to the polyamide. This problem is discussed in an article by Seidenspinner (Galvanotechnik 75 (1984), 852) and various solutions, for example treatment with aqueous hydrochloric acid, are suggested. Galvanotechnik 79 (1988), 54 describes a process for the surface treatment of polyamide injection moldings, in which the surface is first activated in a bath containing palladium salts and then roughened in a bath containing calcium salts and aluminum salts. This process uses expensive materials and is therefore economically disadvantageous on the one hand and on the other hand the adhesive strengths achieved are still not completely satisfactory.
EP-A 56 986 discloses polyamide molding materials which contain from 30 to 60% by weight of wollastonite as a filler and are particularly suitable for metallization. The pretreatment is carried out using a 4-15% strength solution of hydrochloric acid or sulfuric acid, roughening of the surface being achieved through attack on the filler particles, ie. the filler is essential for achieving good adhesion between metal and polyamide. Because of the high filler content, however, the quality of the surface is adversely affected, which is disadvantageous in applications in the decorative sector.
It is an object of the present invention to provide a process for the surface treatment of moldings based on polyamides, which should subsequently be readily metallizable, the said process avoiding the disadvantages described above.